The amygdala is often characterized as an integration center for olfactory and nonolfactory sensory influences on motivated behaviors. Ablation and stimulation studies have demonstrated amygdaloid influences on aggression, defense, mating feeding, and drinking, and anatomical investigations have confirmed input to this area from olfactory and vomeronasal systems and from neocortical areas receiving visual, auditory and somatosensory information indirectly. But scrutiny of the available anatomical data suggests that these sensory systems may be segregated within the amygdaloid complex with little or no overlapping input. This tentative conclusion is based on data that at this time are not complete for any single species. Research proposed here is designed to take the first step in a complete identification of the afferents to the amygdala. This initial survey can be accomplished with horseradish peroxidase injections into the amygdaloid area with subsequent histochemical identification of horseradish peroxidase transported in a retrograde manner from neuron terminals in the amygdala to their cell bodies of origin in other parts of the brain. The hamster is chosen for study because of evidence that the olfactory and vomeronasal system inputs to the amygdala are essential for mating behavior in the male. Further study of this sensory control of sexual behavior by the central nervous system will be directed by an understanding of the anatomical substrate of the behavioral system.